The chief of the world's largest company has been busy countering stagnant sales at his U.S. stores by refilling their shelves with products that were dropped in a marketing and merchandising overhaul. Outside the U.S., where a quarter of Wal-Mart's $408 billion in sales are generated, Duke recently agreed to buy control of South African retailer Massmart for $4.6 billion, a deal that will add nearly 300 new outlets to the company's 4,100-plus international store portfolio.

Executives from Silicon Valley to Hollywood to Wall Street admires his savvy persistence - and his company's cool culture. The secret to the Netflix CEO's success? He never stops looking over his shoulder. More

Michael Dell was 21 when he first appeared in Fortune. Bill Gates made the cover when he was 30. Here's a look back at some of today's biggest business leaders when they were climbing the corporate ladder. More